As it stands now, I have a wireless brake light and turn indicators on my helmet.

http://m.youtube.com/index?&desktop_uri=%2F

Thats them at work. Right now its implemented with a single fio duino and two xbee radios. Any time the brake, right, or left signals fires you get an indication on the helmet to match. Fun stuff.

Now to the question: because I want to use less expensive hardware in version 2 of this design I need to figure out a different way of letting the controller in my helmet know that an input has changed state. Right now I'm making use of the xbee's ability to monitor pin states to let my fio know when the brake or turn signals are on. How do I do this with a radio without the xbees ability monitor pin state? (hoperf radio)

For the record, as it stands now, I have the fio and its xbee radio on the helmet and just the xbee and its power supply in the tail.

Ive entertained the idea of a low cost duino compatible controller in the tail that would convert the brake, right, and left signals into a serial stream that was xmitted over the hoperf radio. But what would that do to the battery life on the helmet side if it was always receiving data??

Pretty cool there. The hoperf modules are allot cheaper and should easily do the job, but I think you'll need a microcontroller on the helmet end. I think right now you just use the Xbee I/O functions? The hoperf radio has an IRQ out so it can wake the micro in the helmet when it receives data. The hoperf radio has a very low current sleep mode. Still, it only uses approx 600uA when on and idle, but as soon as it receives data the current jumps. Still, nice because the radio has a wake-up timer so that it can wake up, look for a signal and then go back to sleep without waking the microcontroller.

I would like to have a 'duino of SOME type on the helmet side, with one of the hoperf radios. (lowpowerlabs has an interesting setup that combines an atmel 328 and hope radio for the low price of 18-ish dollars US which is pretty much perfect.) Then in the tail, I was thinking of using an ATtiny configured to run like a 'duino (per the how-to from MIT's high low tech lab) also coupled with a hoperf radio (these two together would cost around 9 or 10 dollars) plus the extra bits to control the voltage levels on the inputs and to provide power to the whole thing.

What I don't know how to do is replace the xbee's pin change detect feature with something from the hoperf radios.

For anyone unfamiliar with the xbee feature, It's pretty slick: the sending radio will monitor up to 8 pins for a change detect. If a pin goes high on the sending radio (like the tail of a motorcycle) then the corresponding pin on the receiving xbee also goes high, mimicking the state changes in real time. I use one pin for the brake light, one for left and one for right. The hoperf radios sadly do not have this feature. I was thinking that the motorcycle mounted processor could combine the 3 inputs into 3-bit chunks of data and stream that over serial to the helmet...

Or more likely, each input would generate an ascii symbol and the tail processor would send 3-letter "words" to the helmet and the helmet would decode the words and take appropriate action. Is this feasible?? I saw a tutorial the would turn on individual LEDs based on what character was received from a computer but I'm not sure if this is the same or even similar.

It sounds the same.... I think I need to try it. At least read up anyways.

Ideas/comments/notifications that I'm out of my depth? Also, there's some features of the radio I need to delve into it seems.

Sounds like you have a pretty good idea of what you want to do. I would only suggest adding some kind of checksum to the data so that errors don't make it thru. Send the data often even if nothing has changed. I'd probably just treat it like a one-way link and handle it accordingly by assuming most data doesn't make it even though that shouldn't be the case. I think you should add an accelerometer and incorporate the reading into flashing the brake lamps according to how fast you are decelerating. You could possibly use the accelerometer data to figure out when to cancel turn signals.

That's sounds like a really interesting project. And a one that would increase your safety. However i don't understand how do you install the lights and electronics on the helmet without compromise it's integrity?

Do you just Glow the lights? And do put the Xbee in the pads? cause it sounds to me like a lot of radiation near your head....